The weather is getting good here in Kansas and real nice to do a few things with the car. I have my 72 Cutlass Supreme with a 350 from a 69 Cutlass. I've noticed this morning when I started my car, a very slight amount of smoke (maybe grey?) coming out of the exhaust. Also, the insides of my trumpet tips have a good amount of soot inside. That and since I've had the car for a while, I figured it was probably time for an oil change. I wanted to get advice on which oil I should use.

I've read a couple threads saying 10w30 is pretty safe but figured I would double check with what you guys thought.

My engine does have a few upgrades, but is definitely still just used for streets. Linked is a picture if that could change the suggestion.

Thanks in advance.

 

If you are referring to viscosity, the factory recommendations depend on ambient temperatures. 0 degrees F to 60 degrees F = 10W-30 and 10W-40 in a multi-viscosity oil. 20 degrees F and up = 10W-30, 10W-40, 20W-40, and probably 20W-50. Single viscosity SAE 30 can be used above 60 degrees F. Any SAE 5 base oils (5W, 5W-20, etc.) are not recommended for high speed driving. Generally, higher viscosity is better at higher temperatures and lower viscosity is preferred for lower temperatures. If the engine is burning some oil, higher viscosities will reduce oil consumption.
Exhaust "soot" can be caused by many factors.
If the engine has the original style flat faced lifters, try to get an oil with sufficient ZDDP additive in it, or add a supplement. Some current oils have reduced levels. It is needed to avoid lifter and cam wear. Some people think that synthetic oil will compensate for the loss of zinc, but I am unsure. The safest way is to use the zinc compound. It has been "proven" over decades of use.
Also, be sure to use a good filter. Wix, NAPA Gold, and Amsoil seem to be well made. The media probably is a bit "tighter" on the Amsoil, as it is synthetic.